The present invention relates generally to Joule-Thomson valve flow controllers, and more particularly, to a pressure activated Joule-Thomson valve flow controller.
The assignee of the present invention manufactures missile systems that use a focal plane array infrared sensor that requires cooling to approximately 90.degree. K. The temperature of the focal plane array and infrared sensor must be maintained within a few tenths of a degree Kelvin for precise target acquisition. Joule-Thomson coolers using argon or nitrogen gas are employed to cool the focal plane array infrared sensor.
Development of ultra fast cooldown cryostats by the assignee of the present invention has lead to a need for an actuator/flow controller that is compatible therewith. The flow controller is required to permit high flow during cooldown, and reduce flow once cooldown temperature is reached, while permitting a low flow to maintain the temperature of the focal plane array infrared sensor.
Currently available Joule-Thomson valve flow controllers incorporate temperature sensitive devices to control flow. This requires that a temperature sensor or actuator to be located at the cold end of the cryostat. In the case of a Carleton-type design, gas filled bellows are located at the cold end of the cryostat. The bellows collapse as they cool down with the cryostat and dewar assembly. Upon collapse, a valve is closed to limit flow.
One patented valve flow controller developed by the assignee of the present invention incorporates a temperature sensitive snap disk. The snap disk is a bimetallic, and has a convex curvature at room temperature. When cooled down to approximately 90.degree. K, the disk snaps into a concave shape, which, when coupled to a valve system, reduces flow.
In both of the above-described cases, the actuator device must cool to the required (approximately 90.degree. K) temperature before valve closure occurs. These devices rob the cryostat of performance due to the mass of the device (specific heat), which also needs to be cooled to the required temperature.
Accordingly, it is an objective of the present invention to provide for a pressure activated Joule-Thomson valve flow controller.